The present invention is directed to a shaft sealing device for preventing leakage of gas. More particularly, the present invention relates to a new and improved shaft sealing device for eliminating drawbacks present in conventional shaft sealing devices, such as loss of power and malfunctioning of the sealing effect.
A type of conventional shaft sealing device has a mechanical seal situated on the side of gas to be sealed, and a floating ring seal situated on the side of the atmosphere, when viewed in the axial direction. Lubrication liquid having a pressure slightly greater than the pressure of the gas, is supplied between these two seals, to prevent gas leakage in this manner.
FIG. 1 is a vertical sectional view illustrating a conventional shaft sealing device. In FIG. 1, atmosphere is present to the left of a shaft sealing case 2, through which a rotation shaft 1 passes, while a gas chamber is present on the right side thereof. A sealing chamber 5 is formed in the shaft sealing case 2, with the mechanical seal being located on the right side of the sealing chamber 5 (i.e. on the gas chamber side thereof), while the floating ring seal 14 is situated on the left side thereof.
The mechanical seal comprises a rotation ring 7 fitted onto the rotation shaft 1 through an O-ring 6, and fixed by a nut 8 which is screwed onto the rotation shaft 1, and a stationary ring 10 fitted into the shaft sealing case 2 through an O-ring 12 and urged to the left by a compression spring 13. The rotation ring 7 slidably contacts the stationary ring 10 at the slidable face 9 thereof.
The floating ring seal 14 is stopped or held in place by a rotation stopper pin 16 fixed to the shaft sealing case 2.
The rotation shaft 1 is freely rotatably fitted into the floating ring seal 14 with a small clearance interposed between the seal 14 and shaft 1. Additionally, the floating ring seal 14 slidably contacts the shaft sealing case 2 at a contact face 15 thereof.
In the case of a conventional shaft sealing device as described above, turbine oil or the like having a comparatively large viscosity is often used as the lubrication fluid which is supplied to the sealing chamber 5. Viscosity friction loss occurs between rotating portions such as the rotation ring 7, nut 8, and outer circumference of the rotation shaft 1, and the lubrication liquid. This viscosity friction loss causes an extremely large portion of the loss of power in the entire shaft sealing device.
Furthermore, when an end face 7b of the rotation ring 7 vertical (i.e. radial) to the shaft 1 and opposite to the slidable face 9 thereof, is present together with endfaces 8a, 8b of the nut in the sealing chamber 5, the pressure within the sealing chamber 5 between the mechanical seal and the floating ring seal fluctuates, because of pumping effect caused by centrifugal force at these portions. This thereby causes the functioning of the mechanical seal to be adversely affected. An end face 7a continuously extending from the slidable face 9 of the rotation ring 7, is narrow in the radial direction thereof, so that the influence thereof is negligible.